1. Field of the Invention
The present invention concerns coupling an optical fiber to an optical component such as a semiconductor laser diode or a photodiode on the same substrate to form an optical send or receive header.
2. Description of the Prior Art
A first problem to be overcome in making any such coupling is to achieve low coupling losses. This requires extremely accurate location.
In a known coupling method the component is fixed to the substrate first, typically by soldering it in place. In this way its active area is located at a predetermined height above a reference surface of the substrate. This height is as closely equal as possible to that assumed by the core of a coupling optical fiber at one end of this fiber when a cylindrical manipulation surface attached to the fiber is brought into bearing engagement with this reference surface.
This manipulation surface is provided by a cylindrical ferrule in the shape of a body of revolution. The fiber is disposed in the ferrule parallel to its axis but off-center. This enables adjustment of the vertical position, i.e. correction of any height difference between the active area of the component and the core of the fiber. This is simply achieved by rotating the ferrule about its axis in contact with the reference surface. Given the positional accuracy required for good coupling the ferrule must be accurately manufactured.
Transverse and longitudinal adjustments are effected by movement of the ferrule in contact with the reference surface before the coupling fiber is fixed once and for all to the substrate.
The coupling fiber is typically short to facilitate the various adjustments and other manipulations. After it is fixed to the substrate its other end is welded to a longer fiber to be coupled. Known welding processes are such that the resulting weld introduces only low light losses.
A second problem that usually has to be overcome in making any such coupling is to make the optical header which contains the component, a section of the coupling fiber and the components needed for coupling them as small as possible. To this end a small substrate is used.
One object of the present invention is to enable good coupling between an optical component and a coupling fiber within in a compact and low-cost optical header.